This invention relates in general to devices for controlling the shifting of gears within a gearbox. More specifically, this invention relates to an improved structure for a shift lock-out device that selectively enables and disables the occurrence of such gear shifting within a gearbox in response to one or more predetermined operating conditions.
A gearbox is a well known structure that is often provided between a source of rotational energy and a rotatably driven device. In its simplest form, the gearbox selectively provides first and second gear ratios between an input shaft of the gearbox (which is rotatably driven by the source of rotational energy) and an output shaft of the gearbox (which rotatably drives the rotatably driven device). The first gear ratio is provided between the input and output shafts of the gearbox when a first set of gears contained within the gearbox is engaged therebetween, while the second gear ratio is provided between the input and output shafts of the gearbox when a second set of gears contained within the gearbox is engaged therebetween. Typically, a clutch mechanism (such as a conventional axially movable shift collar) is provided within the gearbox for selectively engaging one of the first and second sets of gears for providing the first and second gear ratios.
When the clutch mechanism is actuated to shift from one of the first and second gear ratios to the other, there may be a differential between the rotational speeds of the gears contained in the first and second sets of gears, i.e., one of the gears contained in the first and second sets of gears may be rotating faster or slower than another. Because of this, the rotational speed of the shift collar may differ from the selected gear of the first and second sets of gears to which it is being moved into engagement. It is desirable that this speed differential be minimized to avoid gear grinding or damage to the gears during shifting, particularly when the clutch mechanism is embodied as a conventional shift collar.
Known structures for minimizing this speed differential during shifting include gearbox synchronizers and internal gearbox clutches. Alternatively, an operator may minimize this speed differential manually by carefully controlling the shifting process. However, these known structures and methods may result in wear on friction elements or may require specialized expertise. Thus, it would be desirable to provide an improved device for controlling the shifting of gears within a gearbox that avoids these problems simply and inexpensively.